Integrated fan-out package and manufacturing method thereof

ABSTRACT

An integrated fan-out package includes a die, an encapsulant, a redistribution structure, a seed layer, conductive pillars, and a buffer layer. The encapsulant encapsulates the die. The redistribution structure is over the die and the encapsulant. The redistribution structure includes dielectric layers and conductive patterns. The dielectric layers are sequentially stacked and the conductive patterns are sandwiched between the dielectric layers. The seed layer and the conductive pillars are sequentially stacked over the redistribution structure. The seed layer is directly in contact with the conductive patterns closest to the conductive pillars. The buffer layer is disposed over the redistribution structure. The dielectric layer closest to the conductive pillars and the buffer layer are sandwiched between the seed layer and the conductive patterns closest to the conductive pillars. A Young&#39;s modulus of the buffer layer is higher than a Young&#39;s modulus of each of the dielectric layers of the redistribution structure.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation application of and claims the priority benefit of a prior application Ser. No. 15/730,760, filed on Oct. 12, 2017, now allowed. The entirety of the above-mentioned patent applications is hereby incorporated by reference herein and made a part of this specification.

BACKGROUND

The semiconductor industry has experienced rapid growth due to continuous improvements in the integration density of various electronic components (i.e., transistors, diodes, resistors, capacitors, etc.). For the most part, this improvement in integration density has come from repeated reductions in minimum feature size, which allows more of the smaller components to be integrated into a given area. Currently, integrated fan-out packages are becoming increasingly popular for their compactness. The integrated fan-out packages typically include a redistribution circuit structure laying over the molded integrated circuit devices such that the integrated circuit devices may be accessed. In order to meet the requirements for smaller sizes and higher packing densities, the manufacturing method for the redistribution circuit structure has become an important issue in the field.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the following detailed description when read with the accompanying figures. It is noted that, in accordance with the standard practice in the industry, various features are not drawn to scale. In fact, the dimensions of the various features may be arbitrarily increased or reduced for clarity of discussion.

FIGS. 1A-1F are schematic cross-sectional views illustrating processes of a method for manufacturing an integrated fan-out package in accordance with some embodiments of the disclosure.

FIGS. 2A-2K are schematic enlarged cross-sectional views illustrating processes of a manufacturing method for an exemplary package focused in a region R in accordance with some embodiments of the disclosure.

FIGS. 3A-3J are schematic enlarged cross-sectional views illustrating processes of a manufacturing method for an exemplary package focused in a region R in accordance with some alternative embodiments of the disclosure.

FIGS. 4A-4J are schematic enlarged cross-sectional views illustrating processes of a manufacturing method for an exemplary package focused in a region R in accordance with some alternative embodiments of the disclosure.

FIG. 5A is a schematic enlarged cross-sectional view illustrating an exemplary package focused in a region R in accordance with some alternative embodiments of the disclosure.

FIG. 5B is a schematic top view illustrating the buffer layer and the conductive pillar in FIG. 5A.

FIGS. 6A-6I are schematic enlarged cross-sectional views illustrating processes of a manufacturing method for an exemplary package focused in a region R in accordance with some alternative embodiments of the disclosure.

FIG. 7A is a schematic enlarged cross-sectional view illustrating an exemplary package focused in a region R in accordance with some alternative embodiments of the disclosure.

FIG. 7B is a schematic top view illustrating the buffer layer and the conductive pillar in FIG. 7A.

FIG. 8 is a schematic view illustrating a stacked package structure including the integrated fan-out package in FIG. 1F.

DETAILED DESCRIPTION

The following disclosure provides many different embodiments, or examples, for implementing different features of the provided subject matter. Specific examples of components and arrangements are described below to simplify the present disclosure. These are, of course, merely examples and are not intended to be limiting. For example, the formation of a first feature over or on a second feature in the description that follows may include embodiments in which the first and second features are formed in direct contact, and may also include embodiments in which additional features may be formed between the first and second features, such that the first and second features may not be in direct contact. In addition, the present disclosure may repeat reference numerals and/or letters in the various examples. This repetition is for the purpose of simplicity and clarity and does not in itself dictate a relationship between the various embodiments and/or configurations discussed.

Further, spatially relative terms, such as “beneath,” “below,” “lower,” “above,” “upper” and the like, may be used herein for ease of description to describe one element or feature's relationship to another element(s) or feature(s) as illustrated in the figures. The spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. The apparatus may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein may likewise be interpreted accordingly.

Other features and processes may also be included. For example, testing structures may be included to aid in the verification testing of the 3D packaging or 3DIC devices. The testing structures may include, for example, test pads formed in a redistribution layer or on a substrate that allows the testing of the 3D packaging or 3DIC, the use of probes and/or probe cards, and the like. The verification testing may be performed on intermediate structures as well as the final structure. Additionally, the structures and methods disclosed herein may be used in conjunction with testing methodologies that incorporate intermediate verification of known good dies to increase the yield and decrease costs.

FIGS. 1A-1F are schematic cross-sectional views illustrating processes of a method for manufacturing an integrated fan-out package 10 in accordance with some embodiments of the disclosure. Referring to FIG. 1A, a carrier substrate C having a de-bonding layer DB formed thereon is provided. In some embodiments, the carrier substrate C may be a glass substrate and the de-bonding layer DB may be a light-to-heat conversion (LTHC) release layer formed on the glass substrate. In some embodiments, a dielectric layer (not shown) may be optionally formed over the de-bonding layer DB.

As shown in FIG. 1A, a plurality of dies 100 is provided and placed over the carrier substrate C. In some embodiments, the dies 100 may be placed on the de-bonding layer DB through a pick and place process. The dies 100 may be attached or adhered on the de-bonding layer DB through a die attach film (DAF), an adhesion paste or the like. For simplicity, only one die 100 is illustrated in FIG. 1A. However, more than one dies are provided and may be arranged in an array. It is understood that the scope of the disclosure is not limited by the disclosed example(s). In some embodiments, the current process step may be considered as part of a wafer level packaging process.

In some embodiments, as illustrated in FIG. 1A, each die 100 includes a semiconductor substrate 110, a plurality of conductive pads 120, a passivation layer 130, a post-passivation layer 140, a plurality of conductive posts 150, and a protection layer 160. In some embodiments, the semiconductor substrate 110 may be a silicon substrate including active components (e.g., transistors or the like) and optionally passive components (e.g., resistors, capacitors, inductors or the like) formed therein. The conductive pads 120 are formed on the semiconductor substrate 110 and may be aluminum pads, copper pads or other suitable metal pads. The conductive posts 150 are disposed on the conductive pads 120 and are electrically connected to the conductive pads 120. In some embodiments, the conductive posts 150 are formed on the conductive pads 120 by a plating process of a conductive material. In some embodiments, the conductive posts 150 are plated copper pillars or other suitable metallic pillars. In some alternative embodiments, the conductive posts 150 are copper pillars or other suitable metallic pillars which are covered by solder caps (e.g., lead-free solder caps). In some embodiments, the protection layer 160 may be a polymer layer having sufficient thickness to encapsulate and protect the conductive posts 150. In some embodiments, the material of the protection layer 160 includes polybenzoxazole (PBO), polyimide (PI), or other suitable polymeric material. In some alternative embodiments, the protection layer 160 may be made of inorganic materials. In some embodiments, the post-passivation layer 140 is optional.

Referring to FIG. 1B, an encapsulation material 200 is formed on the de-bonding layer DB to encapsulate the die(s) 100. In other words, all of the dies 100 (only one die is shown in FIG. 1B) are molded and embedded in the encapsulation material 200. In some embodiments, the encapsulation material 200 is formed by a molding process. The conductive posts 150 and the protection layer 160 of the die 100 are fully covered by the encapsulation material 200. In other words, the conductive posts 150 and the protection layer 160 of the die 100 are not revealed and are well protected by the encapsulation material 200. In some alternative embodiments, the material of the encapsulation material 200 includes an epoxy resin or other suitable dielectric materials.

Referring to FIG. 1C, the encapsulation material 200 is then ground until the conductive posts 150 are exposed to form an encapsulant 200 a. In some embodiments, the encapsulation material 200 is ground by a mechanical grinding process and/or a chemical mechanical polishing (CMP) process. During the grinding process of the encapsulation material 200, portions of the protection layer 160 and portions of the conductive posts 150 are ground to form a protection layer 160 a and conductive posts 150 a. As illustrated in FIG. 1C, the encapsulant 200 a surrounds the die(s) 100 a and laterally encapsulates sidewalls of the die(s) 100 a. In other words, sidewalls of the dies 100 a (only one die is shown in FIG. 1C) are surrounded and wrapped by the encapsulant 200 a. In some embodiments, top surface of the encapsulant 200 a, top surfaces of the conductive posts 150 a, and top surface of the protection layer 160 a are substantially coplanar and flush with one another.

Referring to FIG. 1D, a redistribution structure 300 is formed over the encapsulant 200 a and covering the die(s) 100 a. In some embodiments, a seed layer 410 a and a plurality of conductive pillars 420 are later formed on the redistribution structure 300. Thereafter, a plurality of conductive bumps 500 are formed over the conductive pillars 420. In some embodiments, the conductive pillars 420 and the conductive bumps 500 are collectively referred to as controlled collapse chip connect (C4) bumps. In FIG. 1D, a region R is encircled by the dotted line and such region R will be further illustrated to describe the connection between the redistribution structure 300, the conductive pillars 420, and the conductive bumps 500. Such region R may be shown in schematic enlarged views to further describe the manufacturing processes and possible structural alternations in the following paragraphs. In some embodiments, the redistribution structure 300 includes a first dielectric layer 310 a, a second dielectric layer 312 a, a third dielectric layer 314 a, and a fourth dielectric layer 316 a stacked in sequence. In some embodiments, the redistribution structure 300 also includes a plurality of first conductive patterns 320 a, a plurality of second conductive patterns 322 a, and a plurality of third conductive patterns 324 a electrically connected to one another. The first conductive patterns 320 a are sandwiched between the first dielectric layer 310 a and the second dielectric layer 312 a. Similarly, the second conductive patterns 322 a and the third conductive patterns 324 a are respectively sandwiched between the second dielectric layer 312 a and the third dielectric layer 314 a and between the third dielectric layer 314 a and the fourth dielectric layer 316 a. In some embodiments, the redistribution structure 300 is electrically connected to the dies 100 a. For example, the first conductive patterns 320 a may be in contact with the conductive posts 150 a of the die 100 a to render electrical connection between the two. In some embodiments, for the redistribution structure having four dielectric layers, the fourth dielectric layer 316 a is referred to as the dielectric layer farthest away from the dies 100 a in a direction perpendicular to top surfaces 111 of the dies 100 a (only one die is shown in FIG. 1D). In certain embodiments, the dielectric layer farthest away from the die 100 a or the dielectric layer receiving the conductive pillars 420 has a Young's modulus (modulus of elasticity) higher than the other dielectric layers of the redistribution structure 300. Similarly, the third conductive patterns 324 a are referred to as the conductive patterns farthest away from the dies 100 a in the direction perpendicular to top surfaces 111 of the dies 100 a. In some embodiments, the Young's modulus of the fourth dielectric layer 316 a is higher than the Young's modulus of the first dielectric layer 310 a, the second dielectric layer 312 a, and the third dielectric layer 314 a. In some embodiments, a Young's modulus of the fourth dielectric layer 316 a ranges between 0.5 GPa and 150 GPa. On the other hand, Young's modulus of the first dielectric layer 310 a, the second dielectric layer 312 a, and the third dielectric layer 314 a range between 0.1 GPa and 100 GPa. In certain embodiments, the ratio of the Young's modulus of the fourth dielectric layer 316 a to the Young's modulus of the first, second, or third dielectric layer 310 a, 312 a, 314 a ranges from 1.05 to 100. When the ratio of the Young's modulus is below 1.05, the fourth dielectric layer 316 a is not able to endure the stress generated from the conductive pillars 420, thereby causing the conductive patterns in the redistribution structure 300 to deform. On the other hand, when the ratio of the Young's modulus is above 100, the fourth dielectric layer 316 a would exhibit a hardness similar to that of pure silicon, thereby increasing the processing difficulty. In some embodiments, the thickness of the fourth dielectric layer 316 a is larger than the thickness of the first dielectric layer 310 a, the second dielectric layer 312 a, or the third dielectric layer 314 a. In some embodiments, due to the higher Young's modulus, the fourth dielectric layer 316 a is able to alleviate or block the stress from the conductive pillars 420 to the underlying redistribution structure 300, thus protecting the conductive patterns in the redistribution structure 300 from being damaged by stress generated during assembly processes and/or thermal processes. In other words, the fourth dielectric layer 316 a with a higher Young's modulus aids to alleviate the problem of fine line deformation in the redistribution structure 300. Therefore, in some embodiments, the fourth dielectric layer 316 a of the redistribution structure 300 may be referred to as an anti-stress layer. It should be noted that although FIG. 1D depicted four dielectric layers and three conductive pattern layers, this configuration merely serve as an example. In some alternative embodiments, the redistribution structure 300 may include more or less layers of dielectric layer and conductive pattern layers.

As illustrated in FIG. 1D, in some embodiments, the seed layer 410 a is formed before forming the conductive pillars 420 and is sandwiched between the conductive pillars 420 and the redistribution structure 300. In some embodiments, the conductive pillars 420 are electrically connected to the redistribution structure 300. For example, the conductive pillars 420 may be electrically connected to the third conductive patterns 324 a. The descriptions with respect to the formation of the redistribution circuit structure 300, the seed layer 410 a, the conductive pillars 420, and the conductive bumps 500 will be discussed in greater detail later in conjunction with FIGS. 2A-2K, 3A-3J, 4A-4J, 5A, 6A-6I, and 7A.

Referring to FIG. 1E, the integrated fan-out package array including the conductive bumps 500, the conductive pillars 420, the redistribution structure 300, the encapsulant 200 a and the dies 100 a (only one die is shown in FIG. 1F) is de-bonded from the de-bonding layer DB such that the dies 100 a and the encapsulant 200 a are separated from the carrier substrate C. In some embodiments, the de-bonding layer DB (e.g., the LTHC release layer) may be irradiated by an UV laser such that the de-bonding layer DB may be peeled off from the dies 100 a and the encapsulant 200 a to obtain an integrated fan-out package array.

Referring to FIG. 1F, the integrated fan-out package array is diced or singulated to form a plurality of integrated fan-out packages 10. In some embodiments, the dicing process or the singulation process typically involves dicing with a rotating blade or a laser beam. In other words, the dicing or singulation process is, for example, a laser cutting process, a mechanical cutting process, or other suitable processes.

FIGS. 2A-2K are schematic enlarged cross-sectional views illustrating processes of a manufacturing method for an exemplary package focused in a region R in accordance with some embodiments of the disclosure. FIGS. 2A-2K illustrated detailed process steps for forming the redistribution structure 300, the conductive pillars 420, and the conductive bumps 500 on the encapsulant 200 a and dies 100 a similar to the structures depicted in FIGS. 1C-1D. Referring to FIG. 2A, a dielectric material layer 310 is formed over the protection layer 160 a, the conductive posts 150 a, and the encapsulant 200 a. In some embodiments, the material of the dielectric material layer 310 includes polyimide, epoxy resin, acrylic resin, phenol resin, benzocyclobutene (BCB), polybenzoxazole (PBO), or any other suitable polymer-based dielectric material. In some embodiments, the dielectric material layer 310 has a Young's modulus ranges between 0.1 GPa and 100 GPa and has a thickness ranges between 1 μm to 50 μm. The dielectric material layer 310, for example, may be formed by suitable fabrication techniques such as spin-on coating, chemical vapor deposition (CVD), plasma-enhanced chemical vapor deposition (PECVD) or the like.

Referring to FIG. 2B, in some embodiments, the dielectric material layer 310 is patterned to form the first dielectric layer 310 a having a plurality of openings O_(310a). In some embodiments, the openings O_(310a) expose the conductive posts 150 a located underneath the first dielectric layer 310 a. The dielectric material layer 310 may be patterned through a photolithography process and an etching process. Thereafter, the first conductive patterns 320 a are formed over the first dielectric layer 310 a. In some embodiments, the first conductive patterns 320 a extends into the openings O_(310a) to be in contact with the conductive posts 150 a. The first conductive patterns 320 a may be formed by, for example, electroplating, deposition, and/or photolithography and etching. In some embodiments, a material of the first conductive patterns 320 a includes aluminum, titanium, copper, nickel, tungsten, and/or alloys thereof.

Referring to FIG. 2C, the process steps described in the contexts related to FIG. 2B are repeated to sequentially form the second dielectric layer 312 a, the second conductive patterns 322 a, the third dielectric layer 314 a, and the third conductive patterns 324 a. In some embodiments, the materials of the first dielectric layer 310 a, the second dielectric layer 312 a, and the third dielectric layer 314 a may be the same. In some embodiments, the materials of the first dielectric layer 310 a, the second dielectric layer 312 a, and the third dielectric layer 314 a may be different, as long as the Young's modulus thereof fall in the range of 0.1 GPa to 100 GPa. Similarly, the materials of the first conductive patterns 320 a, the second conductive patterns 322 a, and the third conductive patterns 324 a may be the same or different.

Referring to FIG. 2D and FIG. 2E, the fourth dielectric layer 316 a is formed over the third dielectric layer 314 a and the third conductive patterns 324 a. In some embodiments, the fourth dielectric layer 316 a may be formed by first forming a dielectric material layer 316 over the third dielectric layer 314 a and the third conductive patterns 324 a. Subsequently, the dielectric material layer 316 is patterned to form the fourth dielectric layer 316 a having a plurality of openings O_(316a). The openings O_(316a) expose the third conductive patterns 324 a located underneath the fourth dielectric layer 316 a. In some embodiments, the dielectric material layer 316 may be patterned through a photolithography process and an etching process. In some embodiments, a material of the fourth dielectric layer 316 a is different from the materials of the first dielectric layer 310 a, the second dielectric layer 312 a, and the third dielectric layer 314 a. For example, the material of the fourth dielectric layer 316 a may include molding compound materials such as epoxy resins or phenolic resins. In some embodiments, the fourth dielectric layer 316 a may further include fillers. In some embodiments, the material of the fourth dielectric layer 316 a may include polyimide, epoxy resin, acrylic resin, phenol resin, benzocyclobutene (BCB), polybenzoxazole (PBO), or any other suitable polymer-based dielectric material. In some embodiments, the fourth dielectric layer 316 a has a Young's modulus higher than the Young's modulus of the first dielectric layer 310 a, the second dielectric layer 312 a, and the third dielectric layer 314 a. For example, the fourth dielectric layer 316 a may have a Young's modulus ranges between 0.5 GPa and 150 GPa.

Referring to FIG. 2F, in some embodiments, a seed layer 410 is formed covering the openings O_(316a) and over the fourth dielectric layer 316 a. As illustrated in FIG. 2F, the seed layer 410 is formed in a conformal manner covering the profile of the openings O_(316a). That is, the seed layer 410 extends into the openings O_(316a) to cover a bottom surface and sidewalls of the openings O_(316a). The seed layer 410 may be formed through, for example, a sputtering process, a physical vapor deposition (PVD) process, or the like. In some embodiments, the seed layer 410 may include, for example, copper, titanium-copper alloy, or other suitable choice of materials.

Referring to FIG. 2G, a photoresist pattern layer PR is formed over the seed layer 410. In some embodiments, the photoresist pattern layer PR exposes the seed layer 410 located in the openings O_(316a) and exposes at least a portion of the seed layer 410 located on the fourth dielectric layer 316 a and around the openings O_(316a).

Referring to FIG. 2H, in some embodiments, conductive pillars 420 are formed on the seed layer 410 within the openings O_(316a). In some embodiments, a conductive material (not shown) is deposited onto the exposed seed layer 410 to form the conductive pillars 420. Subsequently, a solder material 430 is deposited onto the conductive pillars 420. The conductive pillars 420 and the solder material 430 are located within openings of the photoresist pattern layer PR. In other words, the conductive pillars 420 and the solder material 430 are formed using the photoresist pattern layer PR as a mask. In some embodiments, the conductive material and the solder material 430 may be formed by a plating process. The plating process is, for example, electro-plating, electroless-plating, immersion plating, or the like. In some embodiments, the conductive material includes, for example, copper, copper alloys, or the like.

Referring to FIG. 2I, the photoresist pattern layer PR is removed and portions of the seed layer 410, which are not covered by the conductive pillars 420 and the solder material 430, are exposed. The photoresist pattern layer PR may be removed/stripped through, for example, etching, ashing, or other suitable removal processes.

Referring to FIG. 2J, the seed layer 410 that is not covered by the conductive pillars 420 and the solder material 430 is removed to render a seed layer 410 a sandwiched between the conductive pillars 420 and the fourth dielectric layer 316 a and between the conductive pillars 420 and the third conductive patterns 324 a. The exposed portions of the seed layer 410 may be removed through an etching process. In some embodiments, the material of the conductive pillars 420 may be different from the material of the seed layer 410, so the exposed portion of the seed layer 410 may be removed through selective etching. In some embodiments, the conductive pillars 420 may be divided into a first portion P1 embedded in the fourth dielectric layer 316 a and a second portion P2 over the fourth dielectric layer 316 a. The seed layer 410 a is located between the second portion P2 and the fourth dielectric layer 316 a, between the first portion P1 and the fourth dielectric layer 316 a, and between the first portion P1 and the third conductive patterns 324 a, as illustrated in FIG. 2J. Referring to FIG. 2K, a reflow process is performed on the solder material 430 to transform the solder material 430 into conductive bumps 500. As illustrated in FIG. 2K, the conductive bumps 500 after the reflow process exhibits a hemispherical shape. However, the disclosure is not limited thereto. In some alternative embodiments, the conductive bumps 500 may take other forms after the reflow process.

FIGS. 3A-3J are schematic enlarged cross-sectional views illustrating processes of a manufacturing method for an exemplary package focused in a region R in accordance with some alternative embodiments of the disclosure. FIGS. 3A-3J illustrated detailed process steps for forming the redistribution structure 300, the conductive pillars 420, and the conductive bumps 500 on the encapsulant 200 a and dies 100 a similar to the structures depicted in FIGS. 1C-1D. Referring to FIG. 3A, the first dielectric layer 310 a, the first conductive patterns 320 a, the second dielectric layer 312 a, the second conductive patterns 322 a, the third dielectric layer 314 a, and the third conductive patterns 324 a are sequentially formed on the dies 100 a and the encapsulant 200 a. The process steps for forming these elements are similar to the process steps illustrated in FIGS. 2A-2C, so the detailed description thereof is omitted herein.

Referring to FIG. 3B, a first seed layer 410 is formed on the third dielectric layer 314 a and the third conductive patterns 324 a. The first seed layer 410 may be formed through, for example, a sputtering process, a physical vapor deposition (PVD) process, or the like. In some embodiments, the first seed layer 410 may include, for example, copper, titanium-copper alloy, or other suitable choice of materials.

Referring to FIG. 3C, a first photoresist pattern layer PR1 is formed over the first seed layer 410. In some embodiments, the first photoresist pattern layer PR1 exposes at least a portion of the first seed layer 410 located over the third conductive patterns 324 a.

Referring to FIG. 3D, a first conductive material 420 a is deposited onto the exposed first seed layer 410 using the first photoresist pattern layer PR1 as a mask. In some embodiments, the first conductive material 420 a may be formed by a plating process. The plating process is, for example, electro-plating, electroless-plating, immersion plating, or the like. In some embodiments, the first conductive material 420 a includes, for example, copper, copper alloys, or the like.

Referring to FIG. 3E, the first photoresist pattern layer PR1 is removed and portions of the first seed layer 410, which are not covered by the first conductive material 420 a, are exposed. The first photoresist pattern layer PR1 may be removed/stripped through, for example, etching, ashing, or other suitable removal processes. Subsequently, the first seed layer 410 not covered by the first conductive material 420 a is removed to render a first seed layer 410 a sandwiched between the first conductive material 420 a and the third conductive patterns 324 a. The exposed portion of the first seed layer 410 may be removed through an etching process.

Referring to FIG. 3F, the fourth dielectric layer 316 a is formed around the first seed layer 410 a and the first conductive material 420 a. Similar to the embodiment of FIGS. 2A-2K, in some embodiments, the material of the fourth dielectric layer 316 a is different from the materials of the first dielectric layer 310 a, the second dielectric layer 312 a, and the third dielectric layer 314 a. For example, the fourth dielectric layer 316 a has a Young's modulus higher than the Young's modulus of the first dielectric layer 310 a, the second dielectric layer 312 a, and the third dielectric layer 314 a. In some embodiments, due to higher Young's modulus, the fourth dielectric layer 316 a of the redistribution structure 300 may be referred to as an anti-stress layer.

Referring to FIG. 3G, a second seed layer 412 may be formed over the fourth dielectric layer 316 a and the first conductive material 420 a. Subsequently, a second photoresist pattern layer PR2 is formed over the second seed layer 412. In some embodiments, the second photoresist pattern layer PR2 exposes at least a portion of the second seed layer 412 located on the first conductive material 420 a. The second seed layer 412 may be similar to the first seed layer 410 and the second photoresist pattern layer PR2 may be similar to the first photoresist pattern layer PR1, so the detailed description thereof is omitted herein.

Referring to FIG. 3H, a second conductive material 420 b and a solder material 430 are deposited onto the exposed second seed layer 412 using the second photoresist pattern layer PR2 as a mask. The second conductive material 420 b may be similar to the first conductive material 410 b, so the detailed description thereof is omitted herein.

Referring to FIG. 3I, the second photoresist pattern layer PR2 is removed and portions of the second seed layer 412, which are not covered by the second conductive material 420 b and the solder material 430, are exposed. The second photoresist pattern layer PR2 may be removed/stripped through, for example, etching, ashing, or other suitable removal processes. Subsequently, the second seed layer 412 not covered by the second conductive material 420 b and the solder material 430 is removed to render a second seed layer (additional seed layer) 412 a sandwiched between the second conductive material 420 b and the first conductive material 420 a and between the second conductive material 420 b and the fourth dielectric layer 316 a. The exposed portion of the second seed layer 412 may be removed through an etching process. Referring to FIG. 3I, the first conductive material 420 a and the second conductive material 420 b constitute the conductive pillars 420. In some embodiments, the first conductive material 420 a may be referred to as a first portion P1 of the conductive pillars 420 embedded in the fourth dielectric layer 316 a. On the other hand, the second conductive material 420 b may be referred to as a second portion P2 of the conductive pillars 420 over the fourth dielectric layer 316 a. The first seed layer 410 a is located between the first portion P1 and the third conductive patterns 324 a. The second seed layer 412 a is located between the first portion P1 and the second portion P2 and between the fourth dielectric layer 316 a and the second portion P2. Referring to FIG. 3J, a reflow process is performed on the solder material 430 to transform the solder material 430 into conductive bumps 500.

FIGS. 4A-4J are schematic enlarged cross-sectional views illustrating processes of a manufacturing method for an exemplary package focused in a region R in FIG. 1C in accordance with some alternative embodiments of the disclosure. FIGS. 4A-4J illustrated detailed process steps for forming the redistribution structure 300, the buffer layer 600 a, the conductive pillars 420, and the conductive bumps 500 on the encapsulant 200 a and dies 100 a similar to the structures depicted in FIGS. 1C-1D. Referring to FIG. 4A, the first dielectric layer 310 a, the first conductive patterns 320 a, the second dielectric layer 312 a, the second conductive patterns 322 a, the third dielectric layer 314 a, and the third conductive patterns 324 a are sequentially formed on the dies 100 a and the encapsulant 200 a. The process steps for forming these elements are similar to the process steps illustrated in FIGS. 2A-2C, so the detailed description thereof is omitted herein.

Referring to FIG. 4B and FIG. 4C, the fourth dielectric layer 316 a is formed over the third dielectric layer 314 a and the third conductive patterns 324 a. The fourth dielectric layer 316 a may be formed by first forming a dielectric material layer 316 over the third dielectric layer 314 a and the third conductive patterns 324 a. Subsequently, the dielectric material layer 316 is patterned to form the fourth dielectric layer 316 a having a plurality of openings O_(316a). The openings O_(316a) expose at least a portion of the third conductive patterns 324 a located underneath the fourth dielectric layer 316 a. In some embodiments, the dielectric material layer 316 may be patterned through a photolithography process and an etching process. In some embodiments, the material of the fourth dielectric layer 316 a is the same as the materials of the first dielectric layer 310 a, the second dielectric layer 312 a, and the third dielectric layer 314 a. In some embodiments, the fourth dielectric layer 316 a is referred to as the dielectric layer farthest away from the dies 100 a in the direction perpendicular to top surfaces of the dies 100 a. Similarly, the third conductive patterns 324 a are referred to as the conductive patterns farthest away from the dies 100 a in the direction perpendicular to top surfaces of the dies 100 a. In some embodiments, the first dielectric layer 310 a, the second dielectric layer 312 a, the third dielectric layer 314 a, the fourth dielectric layer 316 a, the first conductive patterns 320 a, the second conductive patterns 322 a, and the third conductive patterns 324 a constitute the redistribution structure 300.

Referring to FIG. 4D, a buffer layer 600 is formed over the fourth dielectric layer 316 a and the third conductive patterns 324 a. In some embodiments, the material of the buffer layer 600 is different from the materials of the first dielectric layer 310 a, the second dielectric layer 312 a, the third dielectric layer 314 a, and the fourth dielectric layer 316 a. For example, the material of the buffer layer 600 may include molding compound materials such as epoxy resins or phenolic resins. In some embodiments, the buffer layer 600 may further include fillers. In some embodiments, the material of the buffer layer 600 may include polyimide, epoxy resin, acrylic resin, phenol resin, benzocyclobutene (BCB), polybenzoxazole (PBO), or any other suitable polymer-based dielectric material. In some embodiments, the buffer layer 600 has a Young's modulus higher than the Young's modulus of the first dielectric layer 310 a, the second dielectric layer 312 a, the third dielectric layer 314 a, and the fourth dielectric layer 316 a. For example, the Young's modulus of the buffer layer 600 ranges between 0.5 GPa and 150 GPa. On the other hand, the Young's modulus of the first dielectric layer 310 a, the second dielectric layer 312 a, the third dielectric layer 314 a, and the fourth dielectric layer 316 a range between 0.1 GPa and 100 GPa. In certain embodiments, the ratio of the Young's modulus of the buffer layer 600 to the Young's modulus of the first, second, third, or fourth dielectric layer 310 a, 312 a, 314 a, 316 a ranges from 1.05 to 100. When the ratio of the Young's modulus is below 1.05, the buffer layer 600 is not able to endure the stress generated from the conductive pillars 420, thereby causing the conductive patterns in the redistribution structure 300 to deform. On the other hand, when the ratio of the Young's modulus is above 100, the buffer layer 600 would exhibit a hardness similar to that of pure silicon, thereby increasing the processing difficulty. In some embodiments, the thickness of the buffer layer 600 is larger than the thickness of the first dielectric layer 310 a, the second dielectric layer 312 a, the third dielectric layer 314 a, or the fourth dielectric layer 316 a. In some embodiments, due to the higher Young's modulus, the buffer layer 600 is able to alleviate or block the stress from the conductive pillars 420 to the underlying redistribution structure 300, thus protecting the conductive patterns in the redistribution structure 300 from being damaged by stress generated during assembly processes and/or thermal processes. In other words, the buffer layer 600 with a higher Young's modulus aids to alleviate the problem of fine line deformation in the redistribution structure 300. Therefore, in some embodiments, the buffer layer 600 may be referred to as an anti-stress layer.

Referring to FIG. 4E, the buffer layer 600 is patterned to form a buffer layer 600 a having a plurality of openings O_(600a). The openings O_(600a) is larger than the openings O_(316a) such that the openings O_(600a) expose the openings O_(316a) of the fourth dielectric layer 316 a and at least a portion of the fourth dielectric layer 316 a.

Referring to FIG. 4F, in some embodiments, a seed layer 410 is formed covering the openings O_(316a) and the openings O_(600a) and over the buffer layer 600 a. As illustrated in FIG. 4F, the seed layer 410 is formed in a conformal manner covering the profiles of the openings O_(316a) and openings O_(600a). That is, the seed layer 410 extends into the openings O_(316a) and openings O_(600a) to cover bottom surfaces and sidewalls of the openings O_(316a) and openings O_(600a). The seed layer 410 may be formed through, for example, a sputtering process, a physical vapor deposition (PVD) process, or the like. In some embodiments, the seed layer 410 may include, for example, copper, titanium-copper alloy, or other suitable choice of materials.

Referring to FIG. 4G, a photoresist pattern layer PR is formed over the seed layer 410. In some embodiments, the photoresist pattern layer PR exposes the seed layer 410 located in the openings O_(316a) and the openings O_(600a). The photoresist pattern layer PR also exposes at least a portion of the seed layer 410 located on the buffer layer 600 a and around the openings O_(600a).

Referring to FIG. 4H, in some embodiments, conductive pillars 420 are formed on the seed layer 410 within the openings O_(316a) and openings O_(600a). In some embodiments, a conductive material (not shown) is deposited onto the exposed seed layer 410 to form the conductive pillars 420. Subsequently, a solder material 430 is deposited onto the conductive pillars 420. In some embodiments, the conductive material and the solder material 430 may be formed by a plating process. The plating process is, for example, electro-plating, electroless-plating, immersion plating, or the like. In some embodiments, the conductive material includes, for example, copper, copper alloys, or the like.

Referring to FIG. 4I, the photoresist pattern layer PR is removed and portions of the seed layer 410, which are not covered by the conductive pillars 420 and the solder material 430, are exposed. The photoresist pattern layer PR may be removed/stripped through, for example, etching, ashing, or other suitable removal processes. Subsequently, the seed layer 410 that is not covered by the conductive pillars 420 and the solder material 430 is removed to render a seed layer 410 a sandwiched between the conductive pillars 420 and the buffer layer 600 a, between the conductive pillars 420 and the fourth dielectric layer 316 a, and between the conductive pillars 420 and the third conductive patterns 324 a. The exposed portion of the seed layer 410 may be removed through an etching process. Referring to FIG. 4J, a reflow process is performed on the solder material 430 to transform the solder material 430 into conductive bumps 500.

FIG. 5A is a schematic enlarged cross-sectional view illustrating an exemplary package focused in a region R in accordance with some alternative embodiments of the disclosure. FIG. 5B is a schematic top view illustrating a buffer layer 600 a and a conductive pillar 420 in FIG. 5A. The structure illustrated in FIG. 5A is similar to the structure illustrated in FIG. 4J except for the location or coverage of the buffer layer 600 a. In other words, the structure illustrated in FIG. 5A may be obtained by the process steps similar to the process steps illustrated in FIGS. 4A-4J, so the detailed description thereof is omitted herein. In some embodiments, an extra step of removing at least a portion of the buffer layer 600 a over the fourth dielectric layer 316 a may be performed to obtain a ring-shaped buffer layer 600 a surrounding the conductive pillars 420. Referring to FIG. 5A and FIG. 5B, the conductive pillars 420 are depicted as round conductive pillars and the ring-shaped buffer layer 600 a surrounding each conductive pillar 420 is depicted as a round ring-shaped doughnut structure as examples for illustration purposes, but are not intended to limit the scope of the disclosure. In some embodiments, each conductive pillar 420 has a maximum diameter of W1. On the other hand, an edge of the ring-shaped buffer layer 600 a and a sidewall of the conductive pillar 420 has a distance of W2. In some embodiments, a ratio of W2 to W1 (W2/W1) ranges between 0.01 and 0.6. Although FIG. 5B illustrated that the conductive pillars 420 are depicted as round cylinders and the buffer layer surrounding the pillars has a corresponding shape, various shapes and different compatible shapes may be adopted, and the disclosure is not limited thereto. In some alternative embodiments, the conductive pillars 420 may be elliptical columns or even square or polygonal columns. Moreover, although FIG. 5A illustrated that the outer sidewalls of the ring-shaped buffer layer 600 a are straight, the disclosure is not limited thereto. In some alternative embodiments, the outer sidewalls of the ring-shaped buffer layer 600 a may be slanted to further enhance the strength of the buffer layer 600 a.

FIGS. 6A-6I are schematic enlarged cross-sectional views illustrating processes of a manufacturing method for an exemplary package focused in a region R in FIG. 1C in accordance with some alternative embodiments of the disclosure. FIGS. 6A-6I illustrated detailed process steps for forming the redistribution structure 300, the buffer layer 600 a, the conductive pillars 420, and the conductive bumps 500 on the encapsulant 200 a and dies 100 a similar to the structures depicted in FIGS. 1C-1D. Referring to FIGS. 6A-6C, the process steps illustrated is similar to the process steps in FIGS. 4A-4C, so the detailed descriptions thereof is omitted herein.

Referring to FIG. 6D, a buffer layer 600 a is formed over the fourth dielectric layer 316 a and the third conductive patterns 324 a. In some embodiments, the buffer layer 600 a extends into the openings O_(316a) to cover sidewalls SW_(316a) of the openings O_(316a). The buffer layer 600 a exposes at least a portion of a bottom surface of the openings O_(316a). In other words, the buffer layer 600 a exposes at least a portion of the third conductive patterns 324 a. In some embodiments, the material of the buffer layer 600 is different from the materials of the first dielectric layer 310 a, the second dielectric layer 312 a, the third dielectric layer 314 a, and the fourth dielectric layer 316 a. For example, the material of the buffer layer 600 a may include molding compound materials such as epoxy resins or phenolic resins. In some embodiments, the buffer layer 600 a may further include fillers. In some embodiments, the material of the buffer layer 600 a may include polyimide, epoxy resin, acrylic resin, phenol resin, benzocyclobutene (BCB), polybenzoxazole (PBO), or any other suitable polymer-based dielectric material. In some embodiments, the buffer layer 600 a has a Young's modulus higher than the Young's modulus of the first dielectric layer 310 a, the second dielectric layer 312 a, the third dielectric layer 314 a, and the fourth dielectric layer 316 a. For example, the Young's modulus of the buffer layer 600 a ranges between 0.5 GPa and 150 GPa. On the other hand, the Young's modulus of the first dielectric layer 310 a, the second dielectric layer 312 a, the third dielectric layer 314 a, and the fourth dielectric layer 316 a range between 0.1 GPa and 100 GPa. In certain embodiments, the ratio of the Young's modulus of the buffer layer 600 a to the Young's modulus of the first, second, third, or fourth dielectric layer 310 a, 312 a, 314 a, 316 a ranges from 1.05 to 100. When the ratio of the Young's modulus is below 1.05, the buffer layer 600 a is not able to endure the stress generated from the conductive pillars 420, thereby causing the conductive patterns in the redistribution structure 300 to deform. On the other hand, when the ratio of the Young's modulus is above 100, the buffer layer 600 a would exhibit a hardness similar to pure silicon, thereby increasing the processing difficulty. In some embodiments, the thickness of the buffer layer 600 a is larger than the thickness of the first dielectric layer 310 a, the second dielectric layer 312 a, the third dielectric layer 314 a, or the fourth dielectric layer 316 a. In some embodiments, due to the higher Young's modulus, the buffer layer 600 a is able to alleviate or block the stress from the conductive pillars 420 to the underlying redistribution structure 300, thus protecting the conductive patterns in the redistribution structure 300 from being damaged by stress generated during assembly processes and/or thermal processes. In other words, the buffer layer 600 a with a higher Young's modulus aids to alleviate the problem of fine line deformation in the redistribution structure 300. Therefore, in some embodiments, the buffer layer 600 a may be referred to as an anti-stress layer.

Referring to FIG. 6E, in some embodiments, a seed layer 410 is formed over the buffer layer 600 a and over the exposed third conductive patterns 324 a. As illustrated in FIG. 6E, the seed layer 410 is formed in a conformal manner. That is, the seed layer 410 extends into the openings O_(316a) to cover the buffer layer 600 a located in the openings O_(316a) and to cover the exposed third conductive patterns 324 a. The seed layer 410 may be formed through, for example, a sputtering process, a physical vapor deposition (PVD) process, or the like. In some embodiments, the seed layer 410 may include, for example, copper, titanium-copper alloy, or other suitable choice of materials.

Referring to FIG. 6F, a photoresist pattern layer PR is formed over the seed layer 410. In some embodiments, the photoresist pattern layer PR exposes the seed layer 410 located in the openings O_(316a). The photoresist pattern layer PR also exposes at least a portion of the seed layer 410 located on the buffer layer 600 a. In some embodiments, the photoresist pattern layer PR may include photosensitive resins.

Referring to FIG. 6G, in some embodiments, conductive pillars 420 are formed on the seed layer 410 over the buffer layer 600 a. In some embodiments, a conductive material (not shown) is deposited onto the exposed seed layer 410 to form the conductive pillars 420. The conductive pillars 420 are in contact with the seed layer 410 located on the third conductive patterns 324 a to render electrical connection with the redistribution structure 300. Subsequently, a solder material 430 is deposited onto the conductive pillars 420. In some embodiments, the conductive material and the solder material 430 may be formed by a plating process. The plating process is, for example, electro-plating, electroless-plating, immersion plating, or the like. In some embodiments, the conductive material includes, for example, copper, copper alloys, or the like.

Referring to FIG. 6H, the photoresist pattern layer PR is removed and portions of the seed layer 410, which are not covered by the conductive pillars 420 and the solder material 430, are exposed. The photoresist pattern layer PR may be removed/stripped through, for example, etching, ashing, or other suitable removal processes. Subsequently, the seed layer 410 that is not covered by the conductive pillars 420 and the solder material 430 is removed to render a seed layer 410 a sandwiched between the conductive pillars 420 and the buffer layer 600 a and between the conductive pillars 420 and the third conductive patterns 324 a. The exposed portion of the seed layer 410 may be removed through an etching process. Referring to FIG. 6I, a reflow process is performed on the solder material 430 to transform the solder material 430 into conductive bumps 500.

FIG. 7A is a schematic enlarged cross-sectional view illustrating an exemplary package focused in a region R in accordance with some alternative embodiments of the disclosure. FIG. 7B is a schematic top view illustrating a buffer layer 600 a and a conductive pillar 420 in FIG. 7A. The structure illustrated in FIG. 7A is similar to the structure illustrated in FIG. 6I except for the location or coverage of the buffer layer 600 a. In other words, the structure illustrated in FIG. 7A may be obtained by the processes similar to the processes illustrated in FIGS. 6A-6I, so the detailed description thereof is omitted herein. In some embodiments, an extra step of removing at least a portion of the buffer layer 600 a over the fourth dielectric layer 316 a may be performed to obtain a ring-shaped buffer layer 600 a surrounding the conductive pillars 420. Referring to FIG. 7A and FIG. 7B, the conductive pillars 420 are depicted as round conductive pillars and the ring-shaped buffer layer 600 a surrounding each conductive pillar 420 is depicted as a round ring-shaped doughnut structure as examples for illustration purposes, but are not intended to limit the scope of the disclosure. In some embodiments, each conductive pillar 420 has a maximum diameter of W1. On the other hand, an edge of the ring-shaped buffer layer 600 a and a sidewall of the conductive pillar 420 has a distance of W2. In some embodiments, a ratio of W2 to W1 (W2/W1) ranges between 0.01 and 0.6. Although FIG. 7B illustrated that the conductive pillars 420 are depicted as round cylinders and the buffer layer surrounding the pillars has a corresponding shape, various shapes and different compatible shapes may be adopted, and the disclosure is not limited thereto. In some alternative embodiments, the conductive pillars 420 may be elliptical columns or even square or polygonal columns. Moreover, although FIG. 7A illustrated that the outer sidewalls of the ring-shaped buffer layer 600 a are straight, the disclosure is not limited thereto. In some alternative embodiments, the outer sidewalls of the ring-shaped buffer layer 600 a may be slanted to further enhance the strength of the buffer layer 600 a.

FIG. 8 is a schematic view illustrating a stacked package structure including the integrated fan-out package 10 in FIG. 1F. Referring to FIG. 8, the integrated fan-out package 10 may be stacked on a substrate 20. In some embodiments, the substrate 20 may be a semiconductor substrate having passive devices or micro-electro-mechanical system (MEMS) devices formed thereon. In some alternative embodiments, the substrate 20 may be an interposer. The integrated fan-out package 10 may be electrically connected to the substrate 20 through the conductive pillars 420 and the conductive bumps 500. In some embodiments, the substrate 20 having the integrated fan-out package 10 thereon may be further disposed on a printed circuit board 30 to form a semiconductor device. The integrated fan-out package 10 may be electrically connected to the printed circuit board 30 through the substrate 20.

In accordance with some embodiments of the disclosure, an integrated fan-out package includes a die, an encapsulant, a redistribution structure, a plurality of conductive pillars, a seed layer, and a plurality of conductive bumps. The encapsulant encapsulates the die. The redistribution structure is over the die and the encapsulant. The redistribution structure is electrically connected to the die and includes a plurality of dielectric layers that are sequentially stacked and a plurality of conductive patterns sandwiched between the dielectric layers. A Young's modulus of the dielectric layer farthest away from the die is higher than a Young's modulus of each of the rest of the dielectric layers. The conductive patterns are electrically connected to each other. The conductive pillars are disposed on and electrically connected to the redistribution structure. The seed layer is located between the conductive pillars and the redistribution structure. The conductive bumps are disposed on the conductive pillars.

In accordance with some alternative embodiments of the disclosure, an integrated fan-out package includes a die, an encapsulant, a redistribution structure, a buffer layer, a plurality of conductive pillars, a seed layer, and a plurality of conductive bumps. The encapsulant encapsulates the die. The redistribution structure is over the die and the encapsulant. The redistribution structure is electrically connected to the die and includes a plurality of dielectric layers that are sequentially stacked and a plurality of conductive patterns sandwiched between the dielectric layers. The buffer layer is over the redistribution structure. A Young's modulus of the buffer layer is higher than a Young's modulus of each of the dielectric layers of the redistribution structure. The conductive pillars are disposed on the buffer layer and are electrically connected to the redistribution structure. The seed layer is located between the conductive pillars and the buffer layer and between the conductive pillars and the redistribution structure. The conductive bumps are disposed on the conductive pillars.

In accordance with some embodiments of the disclosure, a manufacturing method of an integrated fan-out package includes at least the following steps. A die is provided. The die is encapsulated by an encapsulant. A plurality of dielectric layers are formed over the die and the encapsulant. A plurality of conductive patterns are formed. At least part of the conductive patterns is sandwiched between the dielectric layers. The conductive patterns are electrically connected to each other. An anti-stress layer is formed over the dielectric layers. A Young's modulus of the anti-stress layer is higher than a Young's modulus of each of the dielectric layers. A plurality of conductive pillars are formed over the anti-stress layer. A plurality of conductive bumps are formed over the conductive pillars.

In accordance with some embodiments of the disclosure, an integrated fan-out package includes a die, an encapsulant, a redistribution structure, a seed layer, a plurality of conductive pillars, and a buffer layer. The encapsulant encapsulate the die. The redistribution structure is over the die and the encapsulant. The redistribution structure includes a plurality of dielectric layers and a plurality of conductive patterns. The dielectric layers are sequentially stacked. The conductive patterns are sandwiched between the dielectric layers. The seed layer and the conductive pillars are sequentially stacked over the redistribution structure. The seed layer is directly in contact with the conductive patterns closest to the conductive pillars. The buffer layer is disposed over the redistribution structure. The dielectric layer closest to the conductive pillars and the buffer layer are sandwiched between the seed layer and the conductive patterns closest to the conductive pillars. A Young's modulus of the buffer layer is higher than a Young's modulus of each of the dielectric layers of the redistribution structure.

In accordance with some embodiments of the disclosure, an integrated fan-out package includes a die, an encapsulant, a redistribution structure, a first seed layer, a plurality of conductive pillars, and a second seed layer. The encapsulant encapsulates the die. The redistribution structure is over the die and the encapsulant. The redistribution structure includes a plurality of dielectric layers and a plurality of conductive patterns. The dielectric layers are sequentially stacked. A Young's modulus of the dielectric layer farthest away from the die is higher than a Young's modulus of each of the rest of the dielectric layers. The conductive patterns are sandwiched between the dielectric layers. The first seed layer is embedded in the dielectric layer farthest away from the die. The conductive pillars are disposed on the redistribution structure. The conductive pillars include a first portion and a second portion. The first portion is embedded in the dielectric layer farthest away from the die. Sidewalls of the first portion are directly in contact with the dielectric layer farthest away from the die. The second portion is disposed over the first portion and the dielectric layer farthest away from the die. The second seed layer is sandwiched between the first portion and the second portion of the conductive pillar.

In accordance with some embodiments of the disclosure, an integrated fan-out package includes a die, an encapsulant, a redistribution structure, a buffer layer, a seed layer, and a plurality of conductive pillars. The encapsulant encapsulates the die. The redistribution structure is over the die and the encapsulant. The redistribution structure includes a plurality of dielectric layers and a plurality of conductive patterns. The dielectric layers are sequentially stacked. The conductive patterns are sandwiched between the dielectric layers. The buffer layer is over the redistribution structure. A Young's modulus of the buffer layer is higher than a Young's modulus of each of the dielectric layers of the redistribution structure. The seed layer is disposed on the buffer layer and the dielectric layer farthest away from the die. The seed layer has a ladder-shaped bottom surface. The conductive pillars are disposed on the seed layer.

The foregoing outlines features of several embodiments so that those skilled in the art may better understand the aspects of the present disclosure. Those skilled in the art should appreciate that they may readily use the present disclosure as a basis for designing or modifying other processes and structures for carrying out the same purposes and/or achieving the same advantages of the embodiments introduced herein. Those skilled in the art should also realize that such equivalent constructions do not depart from the spirit and scope of the present disclosure, and that they may make various changes, substitutions, and alterations herein without departing from the spirit and scope of the present disclosure. 

What is claimed is:
 1. An integrated fan-out package, comprising: a die; an encapsulant encapsulating the die; a redistribution structure over the die and the encapsulant, comprising: a plurality of dielectric layers that are sequentially stacked; and a plurality of conductive patterns sandwiched between the plurality of dielectric layers; a seed layer and a plurality of conductive pillars sequentially stacked over the redistribution structure, wherein the seed layer is directly in contact with the conductive patterns closest to the conductive pillars; and a buffer layer disposed over the redistribution structure, wherein the dielectric layer closest to the conductive pillars and the buffer layer are sandwiched between the seed layer and the conductive patterns closest to the conductive pillars, and a Young's modulus of the buffer layer is higher than a Young's modulus of each of the plurality of dielectric layers of the redistribution structure.
 2. The integrated fan-out package according to claim 1, further comprising a plurality of conductive bumps disposed on the plurality of conductive pillars.
 3. The integrated fan-out package according to claim 1, wherein the dielectric layer closest to the conductive pillars has a plurality of first openings exposing at least a portion of the conductive patterns closest to the conductive pillars, and the buffer layer has a plurality of second openings located within the plurality of first openings.
 4. The integrated fan-out package according to claim 3, wherein sidewalls of the plurality of first openings and sidewalls of the plurality of second openings have an offset.
 5. The integrated fan-out package according to claim 1, wherein the buffer layer is a ring-shaped structure surrounding the plurality of conductive pillars and exposes at least a portion of the dielectric layer closest to the conductive pillars.
 6. The integrated fan-out package according to claim 5, wherein a ratio of a distance between an edge of the buffer layer and a sidewall of the plurality of conductive pillars to a maximum diameter of the plurality conductive pillars ranges between 0.01 and 0.6.
 7. An integrated fan-out package, comprising: a die; an encapsulant encapsulating the die; a redistribution structure over the die and the encapsulant, comprising: a plurality of dielectric layers that are sequentially stacked, wherein a Young's modulus of the dielectric layer farthest away from the die is higher than a Young's modulus of each of the rest of the dielectric layers; and a plurality of conductive patterns sandwiched between the plurality of dielectric layers; a first seed layer embedded in the dielectric layer farthest away from the die; a plurality of conductive pillars disposed on the redistribution structure, comprising: a first portion embedded in the dielectric layer farthest away from the die, wherein sidewalls of the first portion are directly in contact with the dielectric layer farthest away from the die; and a second portion disposed over the first portion and the dielectric layer farthest away from the die; and a second seed layer sandwiched between the first portion and the second portion of the conductive pillar.
 8. The integrated fan-out package according to claim 7, further comprising a plurality of conductive bumps disposed on the plurality of conductive pillars.
 9. The integrated fan-out package according to claim 7, wherein a ratio of the Young's modulus of the dielectric layer farthest away from the die to the Young's modulus of the rest of the dielectric layers ranges from 1.05 to
 100. 10. The integrated fan-out package according to claim 7, wherein the dielectric layer farthest away from the die comprises a molding compound material.
 11. The integrated fan-out package according to claim 7, wherein the second seed layer is further sandwiched between the second portion and the dielectric layer farthest away from the die.
 12. The integrated fan-out package according to claim 7, wherein the first portion has substantially straight sidewalls.
 13. The integrated fan-out package according to claim 7, wherein sidewalls of the first portion are aligned with sidewalls of the first seed layer.
 14. The integrated fan-out package according to claim 7, wherein the first seed layer is sandwiched between the first portion and the conductive patterns farthest away from the die.
 15. An integrated fan-out package, comprising: a die; an encapsulant encapsulating the die; a redistribution structure over the die and the encapsulant, comprising: a plurality of dielectric layers that are sequentially stacked; and a plurality of conductive patterns sandwiched between the plurality of dielectric layers; a buffer layer over the redistribution structure, wherein a Young's modulus of the buffer layer is higher than a Young's modulus of each of the plurality of dielectric layers of the redistribution structure; a seed layer disposed on the buffer layer and the dielectric layer farthest away from the die, wherein the seed layer has a stair-shaped bottom surface, and the seed layer is in direct contact with a top surface of the dielectric layer farthest away from the die; and a plurality of conducive pillars disposed on the seed layer.
 16. The integrated fan-out package according to claim 15, wherein the dielectric layer farthest away from the die has a plurality of first openings exposing at least a portion of the conductive patterns farthest away from the die, the buffer layer has a plurality of second openings exposing the plurality of first openings, and the plurality of second openings is larger than the plurality of first openings.
 17. The integrated fan-out package according to claim 16, wherein sidewalls of the plurality of first openings and sidewalls of the plurality of second openings have an offset.
 18. The integrated fan-out package according to claim 15, wherein the buffer layer is a ring-shaped structure surrounding the plurality of conductive pillars and exposes at least a portion of the dielectric layer farthest away from the die.
 19. The integrated fan-out package according to claim 18, wherein a ratio of a distance between an edge of the ring-shaped buffer layer and a sidewall of the plurality of conductive pillars to a maximum diameter of the plurality conductive pillars ranges between 0.01 and 0.6.
 20. The integrated fan-out package according to claim 15, wherein the buffer layer comprises a molding compound material. 